High temperature synthesis of new metal oxynitride materials with electronic properties
Date: Monday, 25 November 2024
Time: 11 AM
Venue: Institut de Ciència de Materials de Barcelona (ICMAB, CSIC) - Sala d'Actes MATGAS
Abstract
In this work we have developed a new synthetic approach of perovskite oxynitrides of tantalum and rare earth metals at temperatures between 1200 and 1700 oC in N2 or N2/H2 (95%/5% V/V) atmospheres, controlling the anion content by the starting stoichiometric ratios of metal nitrides, oxides and oxynitride reactants. New oxynitridosilicates of rare earth and alkaline earth cations have been also prepared by a similar method, as host structures to produce luminescent materials. We have prepared the pseudocubic perovskite LaTaON2 using solid state reactions at 1500 oC under N2 that produce samples with high crystallinity, sintering degree and a high dielectric permittivity. We report the synthesis of the perovskite EuTaO2.37N0.63 and the new ferromagnetic triple perovskite Eu3Ta3O3.66N5.34 at 1200°C using N2 or N2/H2 gas and mixtures of EuN, Ta3N5 or TaON and Eu2O3 as reactants. The crystal structure of Eu3Ta3O3.66N5.34 exhibits two different A sites that are occupied by Eu3+ and Eu2+ with partial order along the c axis. We have found the new family layered perovskites with n=1 Ruddlesden-Popper type structure R2TaO4-xNx for R = La, Ce, Nd, Eu and x=2.69, 2.81, 2,54, 1.20 respectively, that were obtained under N2 at temperatures between 1200°C and 1700°C. They are the first examples of rare earth transition metal oxynitrides with n=1 Ruddlesden-Popper structure, and show different crystal structures and magnetic properties. Finally, the synthesis of the new oxynitridosilicates NdEuSiO3N and NdSrSiO3N with ß-K2SO4 structure is reported. Upon excitation at 405 nm, NdEuSiO3N and NdSrSiO3N:Eu, with band gaps 2.37 eV and 3.72 eV respectively, exhibit orange red luminescence with broad emission bands centered between 605 and 639 nm
Supervisor
Amparo Fuertes Miquel
PhD comittee
President: Xermán de la Fuente Leis, Instituto de Nanociencia y Materiales de Aragón (CSIC), Spain
Secretary: Rosa Palacín Peiró, Institut de Ciència de Materials de Barcelona (CSIC), Spain
Vocal: Lourdes Mestres Vila, Facultad de Química, Universitat de Barcelona, Spain
University: Universitat Autònoma de Barcelona (UAB)
PhD Programme: Material Science
